Yesterday, I mentioned an Israeli company for tznuit clothing I like, Kosher Casual. I love the company but there's another site that's in New York state so faster and cheaper shipping.
However, there are some special items my friends and I like at Shell Sheli's. Kiki Riki is a brand name of shells. Quite a few shell stores in Brooklyn carry this brand. The store also sells Linda Leal brand which is more upscale. I have some LL jumpers and have received many compliments on the quality.
It takes some trial and error to discover what size shell (hint, they tend to run small), sleeve length and material work for you. The cotton/spandex shells tend to be the ones I buy most often. The cotton has a natural feel on skin, the bit of spandex keeps it shape, so that it doesn't stretch out. Generally they are a little less expensive than the dressy one I'll describe next. Perfect for wearing around the house or doing errands in everyday clothes. Also this site as much needed and rarely seen, plus sizes.
One that my friends and I especially like are the ones label "dressy shell." These are microfiber and have a little bit of shiny look. Not glittery, metallic shine but when compared to a flat matte cotton look, the microfiber has a little bit more of a fancier appearance. Looks nice with a shabbat dress or under a jumper worn for work. Right now on this site, they are the same price as the regular shells, often times dressy shells are a bit more expensive which is why I don't buy these as often. However, I'm going purchase the dressy ones while they are the same price.
The other product that I think would be great for those upgrading their current wardrobe to tznuit standards is the dress/skirt extender. This is a fairly new product as a few years back, I had a lot of difficulty kosher-izing my wardrobe as a lot my dress hit right at the knee when standing, which means my full knee was often exposed when sitting. Not good and I felt awful having to replace otherwise nice clothes I liked for longer substitutes. Later on, I found out a lot of women will just wear a longer black skirt undernearth. This does work, except that it adds bulk with having a double waistband of two skirts. There's also "matching" the style of a skirt with the underskirt. These skirt extenders work beautifully, as instead of the bulk of a skirt, there's a thin elastic slip band and 8" of fabric, so that even a mini-skirt can be made kosher with the extender. For me, the extender winders up making the just right at the knees skirt to mid calf, though if I wore the extender further down waist to hips, I could get to almost ankle length.
Just a caveat, the layering dress is tempting, I know since it solves not just knees, but also sleeves and high neck coverage. BUT I don't recommend the Kiki Riki brand layer dress except on very petite women. I am 5'5" but a bit zaftig, and found the layer dress to be cutting too close to full knee coverage without my worrying and feeling I should tug at it.
Instead for the layering dress from Shell Sheli's, purchase a similar item from Kosher Casual. Even with paying for shipping it will be cheaper than the one at Shell Sheli's. The one from Kosher Casual is a very nice layer dress, comes in white, black or brown (nice to see another color) and does nicely cover knee when sitting. I also like how as a one piece dress, the top half doesn't ride up as sometimes a top shell does.